Scientists at King Abdullah University of Science and Technology have discovered bacteria in the ocean that digest PET plastic using specialized enzymes marked by a unique M5 motif. These microbes, found in nearly 80% of global ocean samples, represent nature's adaptation to human pollution. The findings could aid efforts to develop efficient plastic recycling solutions.
Far beneath the ocean's surface, researchers have identified bacteria equipped with enzymes that break down polyethylene terephthalate (PET), the durable plastic in bottles and fabrics. A global study led by Carlos Duarte and Intikhab Alam at KAUST analyzed over 400 ocean samples, revealing these plastic-degrading PETases in nearly 80% of tested waters, from surface gyres to depths of two kilometers.
The key to their function is the M5 motif, a structural feature that distinguishes effective PETases from inactive variants. "The M5 motif acts like a fingerprint that tells us when a PETase is likely to be functional, able to break down PET plastic," Duarte, a marine ecologist, explained. This motif evolved from enzymes that degrade hydrocarbons, allowing microbes to exploit plastic as a scarce carbon source in the ocean.
The discovery builds on a 2016 finding of a plastic-consuming bacterium in a Japanese recycling plant, but confirms oceanic microbes have independently developed similar capabilities. Using AI modeling, genetic screening, and lab tests, the team showed M5-equipped bacteria efficiently dismantle PET. In polluted deep-sea areas, this trait may provide a survival edge, as Alam noted.
While highlighting microbial resilience, Duarte cautioned that breakdown is too slow to counter annual plastic influx. "By the time plastics reach the deep sea, the risks to marine life and human consumers have already been inflicted," he warned. On land, the M5 motif offers a blueprint for engineering faster enzymes to enhance recycling in treatment plants and beyond.
The research, published in The ISME Journal in 2025, underscores a planetary evolutionary response to pollution.